1. Technical Field of the Invention
The present invention relates generally to electric rotating machines. More particularly, the invention relates to a motor-generator for a hybrid vehicle, which includes a stator having an annular stator core and a stator coil wound on the stator core, an inner rotor located radially inward of the stator with an air gap formed therebetween, and an outer rotor located radially outward of the stator with an air gap formed therebetween.
2. Description of the Related Art
Japanese Patent First Publication No. 2008-312288 discloses a motor-generator for use in a hybrid vehicle.
Specifically, as shown in FIG. 1, a drive unit installed in the hybrid vehicle includes the motor-generator 100, a housing 200, a speed reducer 300, a differential mechanism 400, and a drive shaft-receiving portion 500.
The motor-generator 100 is an electric rotating machine that can function both as an electric motor and as an electric generator. The motor-generator 100 includes a rotating shaft 110 that is rotatably supported by the housing 200 via bearings 120, a rotor 130 mounted on the rotating shaft 110, and a stator 140 disposed to surround the rotor 130.
The rotor 130 includes a rotor core 131 and permanent magnets 132 embedded in the rotor core 131. The rotor core 131 is formed by laminating a plurality of magnetic material sheets, such as iron sheets and iron-alloy sheets. The permanent magnets 132 are located in close vicinity to the radially outer periphery of the rotor core 131 and spaced in the circumferential direction of the rotor core 131 at substantially equal intervals.
The stator 140 includes an annular stator core 141, a three-phase stator coil 142 mounted on the stator core 141, and bus bars 143 connected to the stator coil 142. The bus bars 143 are further connected to a power supply cable 220 via a terminal block 210 mounted to the housing 200. Consequently, the stator coil 142 is electrically connected to an external power source 230 via the bus bars 143, the terminal block 210, and the power supply cable 220.
The stator core 141 is formed by laminating a plurality of magnetic material sheets, such as iron sheets and iron-alloy sheets. The stator coil 142 consists of U-phase, V-phase, and W-phase stator windings that are wound on the stator core 141 so as to be offset from each other in the circumferential direction of the stator core 141. The bus bars 143 include U-phase, V-phase, and W-phase bus bars that are respectively connected to the U-phase, V-phase, and W-phase stator windings of the stator coil 142.
The power supply cable 220 is a three-phase cable that consists of U-phase, V-phase, and W-phase cables. The U-phase, V-phase, and W-phase cables are respectively connected to the U-phase, V-phase, and W-phase bus bars 143.
When the hybrid vehicle operates in a normal running mode, the torque that is generated by the motor-generator 100 in its motor mode is transmitted to the drive shaft-receiving portion 500 via the speed reducer 300 and the differential mechanism 400. The torque transmitted to the drive shaft-receiving portion 500 is further transmitted to drive wheels of the hybrid vehicle via a draft shaft (not shown) received by the drive-shaft receiving portion 500, thereby driving the vehicle to run.
Moreover, when the hybrid vehicle operates in a regenerative braking mode, the drive wheels of the vehicle are rotated by the inertial force of the vehicle. In this case, the motor-generator 100 operates in its generator mode to generate electric power with the torque that is transmitted from the drive wheels to the motor-generator 100 via the drive shaft, the drive-shaft receiving portion 500, the differential mechanism 400, and the speed reducer 300. The electric power generated by the motor-generator 100 is then stored in a battery (not shown) of the vehicle via an inverter (not shown).
FIG. 2 shows a cross-section of the stator 140 perpendicular to the axial direction of the stator core 141. As seen from FIG. 2, the stator core 141 includes a plurality of stator teeth 141A that are arranged in the circumferential direction of the stator core 141 at equal intervals. Around each of the stator teeth 141A, there is wound one of the U-phase, V-phase, and W-phase stator windings of the stator coil 142 via an insulator 144A. That is to say, the stator 140 is a so-called concentrated winding stator.
Moreover, as shown in FIG. 2, the stator core 141 further includes a back core portion 141B that are located radially outside of the stator teeth 141A to connect all of the stator teeth 141A together. However, with the back core portion 141B, the radial size of the stator core 141 is increased, thereby making it difficult to downsize the motor-generator 100.